The present invention relates generally to arc fault detection in three phase aircraft power systems and more specifically, to the detection of high level arc faults in these systems.
Increasing age of aircraft used by the aviation industry has prompted many improvements to existing designs and retrofits to improve aircraft safety. A number of fires aboard aircraft have prompted considerable review of the safety of aircraft electrical systems. These reviews have identified arc fault in aircraft power systems as a pressing safety concern. An arc fault is a self sustaining discharge of electricity in a highly conductive ionized gas that results in unintended current flow between conductors. Causes of arc faults in aircraft include wire chafing, dust build up and moisture. The current generated by an arc is limited by the parameters of the circuits to which the conductors belong. High level arcs result when the current generated by the arc exceeds the load current of the circuit. The circuit load current is the current supplied to the load, when the system is in a steady state and in the absence of any faults. High level arcs can also be characterized by imbalances or differences between the three current phases. Arcs generating currents that do not exceed the circuit load current are referred to as low level arcs.
Where possible, the aviation industry has relied upon aircraft circuit breakers to protect against arc faults. These devices are typically designed to protect wiring from thermal damage that occurs during an over-current situation. In three phase aircraft power systems, such as the 115V, 400 Hz, three phase electrical systems used on many aircraft, an arc fault can add to an existing load current causing a fast three-phase imbalance. This fast three phase imbalance is often too short lived to be detected by many aircraft circuit breakers. Research has shown that arc faults giving rise to temperatures as high as 6000° C. can go undetected by aircraft circuit breakers.